In environments that allow for multiple behavioral paths, humans are noteworthy for their ability to adapt to changes in internal goals or external stimuli. The selection of a particular behavior in the face of competing possible actions is the purview of executive control (Logan, 1985). The overarching goals of the proposed research are to examine the factors that influence a person's choice to carry out a particular task and to develop a formal model of task choice in multitask environments. The research will use the recently developed voluntary task switching (VTS) paradigm, in which subjects choose which task to perform on each trial in a multitask environment (Arrington &Logan, 2004a;2005). Unlike standard task switching paradigms, VTS allows the researcher to examine control processes in an environment that involves selection of a task as well as performance when switching tasks, thus providing a new measure of executive control: task choice. The specific aims of the three projects in the proposed research are to examine the influences of external stimuli and internal goal setting on task choice. Project 1 isolates external and internal influences on task choice by parametrically manipulating two different timing intervals. The onset time for the stimuli that afford each task will be manipulated to examine the effect of external stimulus availability on task choice;while, the amount of time between trials will be manipulated to examine the effect of preparation time, allowing for top-down goal setting, on task choice. Projects 2 and 3 follow up with new empirical investigations developed to test specific components of internal control over task choice. Project 2 examines the role of object selection and Project 3 investigates the frequency with which each task is to be performed. Each of the projects will combine collection of behavioral data and mathematical modeling of the cognitive processes that guide task choice within Logan's model of Executive Control of Bundesen's (1990) Theory of Visual Attention (ECTVA;Logan &Gordon, 2001). Within ECTVA, the process of selecting and categorizing a stimulus is conceived of as a race with the winner determined by the processing rates for all possible categorizations. At the simplest level, the processing rate results from a combination of two parameters: a bias to respond with a particular categorization and the evidence provided by the external stimulus for that categorization. The bias parameter is determined through executive control and represents goal setting. The evidence parameter results from the external stimuli. Thus, ECTVA is ideally suited for modeling the internal and external factors influencing task choice. The development of a formal model of task choice will provide a framework for research into the neurophysiology of volitional behavior aimed at elucidating the contributions of lateral and medial neural circuits (Haggard, 2008). It may also further understanding of choice processes in specific populations with deficits in behavioral control (e.g. frontal lobe damage, schizophrenia, or ADHD). PUBLIC HEALTH RELEVANCE: The behavioral choices that individuals make can have significant impact on their physical and mental health;furthermore, disorders affecting behavioral control have dramatic consequence for both individuals and society. The proposed research combines collection of behavioral data with mathematical modeling to examine external, stimulus-based factors and internal, goal-setting factors that influence the choice to perform a particular task in a multitask environment. The development of a formal model of task choice will provide a framework for advancing theoretically-driven research into the neural circuits that underlie volitional behavior and mental disorders involving deficits in behavioral control.